The present invention relates to an arrangement for mixing and treating powdered and granular material by means of compressed gas, and a mechanically driven mixing device with an upright cylindrical mixing tank. The tank has an intake for the material to be mixed, and an outlet for the mixed material, and a flat bottom.
There are already known in the art various mixing devices which produce the mixing effect through the introduction of compressed air into the mixing tank. The compressed air is introduced either through sintered bottoms or directed nozzles.
While, in mixers with sintered bottoms, the mixing is accomplished at pressures up to 10,000 mm of water column, for mixers with directed air nozzles much higher pressures--between 5 and 50 atmospheres gauge are necessary. Here air exit speeds beyond the speed of sound develop at the nozzle ends.
Mixers with sintered bottoms have the disadvantage that with different mixing materials, such as lead dust and soot, or different granulations, e.g., dustlike and granular products, perfect mixing cannot be achieved. It may even happen that the material is sorted out, so that the coarse components remain on the sintered bottom and the fine components escape upward. Another disadvantage is that the admitted air escapes by way of canals forming in the material so that the product not affected, balls up or coalesces and can no longer be mixed.
It is also already known in the art, to mix and homogenize dry powdery materials by introducing compressed air into a mixing tank through a sintered bottom and simultaneously keeping the material to be mixed in motion by mechanically-driven stirring paddles (German Disclosure No. 1,027,966). However, such a device can be used only for completely dry, finely powdered material.
In the case of mixers with directed air jets where the air is introduced at high speed, there may take place a grinding effect at the nozzle end so that the structure of the material is changed. The power required for generating the compressed air is very large and continual maintenance work on the equipment is unavoidable. The tank walls are subject to heavy wear. The filters used for the escape of the air are under a heavy load.
In addition, expensive equipment as, for example, compressors, tanks where the air is stored, and high-pressure lines are necessary.
It is, therefore, an object of the present invention to avoid the disadvantages of conventional mixing devices.
It is a particular object of the present invention to provide a device for mixing and treating powdered and granular material requiring minimum power, minimum wear, and minimum maintenance.
Another object of the present invention is to provide a mixing arrangement for powdered and granular material of the foregoing character, which has a long operating life and may be maintained in service economically.
A further object of the present invention is to provide an arrangement, as described, which is simple in design and construction and may be fabricated at substantially low cost.